Conventional propelled machines may generally include an internal combustion engine that is mechanically coupled through a transmission assembly and drivetrain to the driven wheels or sprockets of the machine. In contrast, propelled machines having electric drive systems include an internal combustion engine that is mechanically coupled to drive a generator that creates electrical power. The power from the generator is then consumed by a motor that is mechanically coupled to drive the wheels or sprockets of the propelled machine. Accordingly, the generator and motor of the electric drive systems can replace the mechanical transmission and drivetrain of conventional internal combustion engine driven machines. This may result in a propelled machine with superior drivetrain efficiency and improved propulsion performance, which correlates to a machine having greater fuel economy and reduced emissions.
The efficiency of the electric drive system, however, is so efficient that the retarding performance of the propelled vehicle becomes an issue. Retarding performance of a propelled machine relates to the capability of the propelled machine to dissipate undesired power or energy. Such undesired power may include the power of the machine when moving at an undesired speed and/or direction. For example, undesired power of the machine can result from travel down a incline, or exist just after the initiation of a directional shift of the machine from a reverse direction to a forward direction, or visa versa.
Conventional propelled machines having mechanical transmissions and drivetrains dissipate portions of undesired power as heat by way of mechanical clutches, torque converters and the engine. In contrast, the electric generator and electric motor of an electric drive machine are extremely efficient components, and thus, by themselves, do not dissipate undesired power well.
U.S. Pat. No. 5,954,799 to Bernd Dietzel (“the '799 patent”) discloses a propelled vehicle having a process for influencing the drag torque of an electric drive system. The process includes the use of an electric drive system having a reversible generator and two reversible electric motors. The electric motors can act as generators and produce electrical power in response to energy acting to rotate the tires of the machine. The generated electrical power may then be supplied to the generator, which can then act as a motor to drive the internal combustion engine. The driving of the internal combustion engine by the generator at a speed of rotation equal to an idling speed of the engine serves to improve the fuel efficiency of the vehicle by obviating the need to inject fuel into the engine.
The '799 patent is generally directed to maintaining a desired speed of the vehicle, but does not disclose maximizing the possible drag torque of the electric drive system in the instance of complete braking of the vehicle or a complete hierarchy of power dissipating devices. Accordingly, the '799 patent does not provide, for example, a complete retarding strategy for dissipating undesired power in a propelled machine having an electric drive.
The present invention avoids some or all of the aforesaid shortcomings in the prior art.